Ignition safety device for induction fired rockets



J ne 1953 c. F. BJORK EI'AL IGNITION SAFETY DEVICE FOR INDUCTION FIRED ROCKETS Filed Dec. 18, 1946 grwe/rvbou- EUTEIlli liicl rk Miczhuel F'Euny gdwf mww Patented June 2, 1953 IGNITION SAFETY DEVICE FOR INDUCTION FIRED ROCKETS Carold F. Bjork, Luke, Md., and Michael F. Bondy, Watertown, Mass., assignors to the United States of America as represented by the Secrotary of War Application December 18, 1946, Serial No. 717,038 1 Claim. (01. 102-49) This invention relates to an improved method and apparatus for igniting ordnance devices, and more particularly for igniting sealed rocket projectiles by electro-magnetic induction.

Ignition of rocket projectiles by percussion has been supplanted in the art by electrical methods. However, the use of electricity in firing rockets has also presented several drawbacks. Due to the necessity for leading ignition wires from the interior of a rocket motor to a connector on the launching apparatus, it becomes difiicult to eiiectively seal the rocket motor against the entry of air or moisture both of which are harmful to the propellent charge. Moreover, time-consuming delays are often encountered in making the proper electrical connections and in addition positive operation is rendered uncertain due to the occasional accidental grounding of the lead wires.

But in the electro-magnetic induction system of the present invention, the necessity for ignition lead wires is eliminated. Positive ignition of a rocket motor is brought about by a secondary coil positioned within a sealed propellent chamber, the voltage necessary for such secondary launching apparatus.

It is a still further object of this invention to provide a safe electrical ignition system for firing rocket projectiles. That is to say, a system whereby the rocket projectile must first be placed into proper firing position within or on a launching apparatus before ignition can be brought about. I

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. 1 is a fragmentary longitudinal sectional view of a rocket and rocket launching apparatus embodying this invention.

Fig. 1a is a similar view of the nozzle end of the ordnance shown in Fig. 1.

Fig. 2 is a diagrammatic view of a modified form of electro-magnetic apparatus for igniting sealed ordnance.

In Fig. 1 is shown a rocket launching tube I in which is contained a rocket motor comprising a head 2 adapted to hold a pay load, a casing 3 outlining a cylindrical combustion chamber 4 and secured to head 2 as by threads 30, and a nozzle 5 shown in Fig. 1a preferably of Venturi construction extending rearwardly from combustion chamber 4. A central burster tube 6 communicates with head 2 and extends axially through chamber 4 to the vicinity of nozzle 5. The propellent charge I surrounds burster tube I5 and preferably comprises cylindrical grains of doublebase powder supported on trap wires 8, the forward ends of which are secured to a ring member 3 I.

A belt type igniter 9 of ethyl cellulose material or the like filled with black powder encircles the propellent charge 1 preferably near the front end of combustion chamber I. Embedded within such fiat belt igniter 9 is an igniting squib III of conventional design. A coil II constituting the secondary of the induction firing system is wound around igniter 9 and is connected to squib II) by lead wires I2. Other lead wires32 extend from igniter 9 and terminate in a single pole, double throw switch l3 contained within a plug I4 which hermetically seals nozzle 5. Switch I3 is operated by a thumbscrew I5 as will be later explained.

The primary coil I6 is wound on the outside of launching tube I at a position concentric with secondary coil I I when the rocket or projectile is located within tube I at the firing position. A source of electricity I I, such as a battery or generator, and a firing key switch I8 are providedior electrical actuation of primary cell I6. A protective shield I9 designed to ward ofi the influence of any stray magnetic fields surrounds primary coil I6.

As shown in Fig. La, switch I3 serves as a safety device to prevent premature operation of the firing circuit. When thumbscrew I5 is tight against the outside wall of plug I4, switch I3 is held closed. Thus the circuit to secondary coil I I is open and squib I 0 is short-circuited thereby preventing accidental energizing of the firing circuit. When thumbscrew I5 is loosened or removed, the spring tension of switch I3 opens the squib contacts and closes the coil contacts. Voltage sufflcient to fire squib I0 can then be induced by the electricity flowing through primary coil I6. The steel casing 3 of the rocket motor also prevents premature inductive firing of erated 'whi'c-h byz their passage through the Venturi orifice or the nozzle produce: a forward imthe rocket by shielding the secondary coil I I from extraneous sources liable to yield a magnetic flux, such as high tension power lines, for example.

Referring to the modification illustrated diagrammatically in Fig-2, it willbeinoted that the primary-coil 20 *neednot surround and be concentric with rocket 2| and launching tube 22. Instead, the primary coil 20 can be placed away from tube 22 in any convenient-amounting ear-l rangement. As in the Fig. 1 construction -abate tery or generator 23 and afiring switch 24 are connected to the primary coil 20.' Howeven in this modification, the primary coilZii'.isprovideti with an internal core 25 and'a shieldfdonthe side away from launching tube 22. The mag- We claim:

In an induction-fired rocket, a tubular casing having a rearwardly-directed Venturi nozzle, a propellent charge in said casing, an induction coil in said casing, an electrically-initiable fuze in :said "casing in ifiring lre1ation"-w ith;said charge, ,a :dielectric pluglremovablyifitting saictnozzle and closing the same, a switch mounted on said plug and comprising first and second opposed contacts netic field of coil 2!; will passintotherocketmotor 2| as shown by dotted lines 27! and thence induce voltage in the secondary coil (not shown) within therocket motor 2 l "The modification-above described isparticularlyuseful for firing rocket projectile ;mounted.in "multiple launching apparatus such as can beutilize'don airplanes and'the 'like. "In such appa- "ratus,'a plurality of launching tubescontaining rockets may be carried on an endless'belt arrangement for individual or automatic firin cby 'electro-magn-etic induction as each launcher .is moved into a firing position adjacent the pri- -It 'appears unnecessary to describe the-mode of yoperation of thi'sin'vention in more detail since "the principles are well known inthe art. The passage of an alternating ,or a suitable directcurrent-through primary coil '16 induces a voltage 'impulse in the'secondary coil '11 sealed within the rocket to set oil a squib ll Ignition ofsquib 1-0ietransf'erred by the-belt igniter 9 to the propellent powder grains '7 Gases are thereby gen- -pe1ling movement of' the'rocket.

It is desire'd to emphasize'that' the "apparatus sand method described above eliminate the use 70f lead-wires extending out of thezrocketprojecfiIe- 'and hence permiteffective sealing/against moisture and air :deleterious to the propellant charge. "Uncertain :connections and the: delays inherent: in' such connections are also noneexi'stent in the induction method of firing :ordn'ance.

50 March, 1945 page=23.

Number andiantarm movable selectively to alternatively engag either of said contacts, a first circuit including said fuze, first contact and switch arm, in series, a second circuit including said inductioncoil'jfuzdseccnd contact and switch arm in series, andimeans-"carried by said plug and normally holding said arm and first contact in en- .;.gagement to close-said first circuit, said means being, manually operable from the exterior of said rocket to effect engagement between said arm and second contact whereby said first circuit is opened and said :second circuit r is closedmtorconnecttsaid fume and coiI in series, saidi'plug; and? switch; being blown outin response' to initiation oi saidxcharge.

CAROLD E. BJORK.

MICHAEL F.1BO'NDY.

lltefereneesccited :in the ,file .of this patent UNITED "STATES PATENTS OTHER. REFERENCES American. .Rifieman, fMagazine, issue 40f 

